PARIS — Marine Le Pen’s concession speech after her National Front party lost in every region of France on Sunday was anything but conciliatory, despite more than 70 percent of voters rejecting the far-right leader’s message of hostility toward immigrants and open borders.

That bristly intransigence, analysts say, is the key to both the National Front’s history and its destiny, and the reason — in the absence of truly dire economic conditions — that a takeover by the far right in France is not likely anytime soon.

What gives the party its fiercely loyal following — its vituperative denunciation of migrants, its unconcealed hostility toward Muslims, its xenophobic “France for the French” message — also makes it an impossible partner for any political group closer to the mainstream and helps block its advancement as a political force.

Throughout the country, in Sunday’s second round of regional voting, the mainstream parties formed a de facto alliance against the National Front, which even lost in the two regions where Ms. Le Pen and her niece Marion Maréchal Le Pen were favored to win.

In those areas, in the deindustrializing, high-unemployment north and in a south full of those who still regret the loss of French Algeria, the third-finishing Socialist Party pulled out of the race, allowing the mainstream right party of the former president, Nicolas Sarkozy, to win.

Permanent outsider status for the National Front — outside the “golden palaces of the Republic,” as Ms. Le Pen sneered Sunday — was the result. A similar dynamic was in play in departmental elections in March, when over half of the left’s voters switched to the mainstream right candidate in the second round, and the right went on to win 535 out of 538 contests with the National Front.

Jérôme Fourquet, a polling expert, noted that the “Republican front was effective, as a big proportion of the left’s voters voted for the right,” meaning Mr. Sarkozy’s party. In the southern region around Nice, 65 percent of those who voted Socialist in the first round voted for the right’s candidate in the second, and in the north around Lille, where Ms. Le Pen was running, the figure was 70 percent, Mr. Fourquet said at a news conference.

The gravelly voiced party leader, perpetually sucking on an electronic cigarette, appears to both revel in that status and to be embittered by it. And since she represents the “courageous and determined patriots,” defeat is never her party’s fault. Nevermind the big turnout Sunday — jumping by more than eight percentage points between the first and second rounds, suggesting an electorate mobilized to beat her — and the lopsided rejection.

Instead, she was the victim of a conspiracy, she told her disappointed supporters in the strangely high-flown language that is the uneasy bearer of her populist message.

Sunday’s loss “revealed the fundamental lie on which has rested for decades the French political system,” Ms. Le Pen said. What was “revealed with no possible ambiguity were the hitherto occult connections of those who claim to oppose each other but who, in reality, share power, without ever resolving your problems, and worse, lead the country, from one mandate to another, into submersion” by migrants “and into chaos.”

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Marion Maréchal-Le Pen, a candidate with France’s far-right National Front Party, spoke to supporters after losing her bid for election in the Provence-Alpes-Côte d’Azur region.Published OnDec. 14, 2015CreditImage by Clement Mahoudeau/European Pressphoto Agency

In other words, the two mainstream parties, the Socialists and the Republicans, ganged up on her, and she lost.

The party “doesn’t realize that in order to win power, it has to make allies and expand its audience,” said Sylvain Crépon, a political scientist and an expert on the National Front. “You can see the limits of its strategy. Any alliance with the right is impossible,” he added.

To be sure, Sunday’s election was not a total loss for the party. It tripled the number of councilors who will sit on the country’s regional assemblies, to 358, providing a potent carrier for the party’s message. And it scored a record number of votes, 6.8 million — 400,000 more than the previous record in the 2012 presidential election.

Ms. Le Pen made it clear that she is looking forward to the 2017 presidential election. “In relation to 2017, she is clearly positioning herself,” said Valérie Igounet, a historian who specializes in the National Front. The party’s “political representatives are now spreading themselves out all over France,” she said.

But Ms. Le Pen will face the same hurdle then. “Their ideas continue to repulse over 70 percent of the French,” Mr. Crépon said.

Both right and left freely steal from the National Front’s ideas, with the left often sounding law-and-order themes and the right vowing to crack down on immigration. “The other two parties wage their campaigns around the Front’s ideas,” Mr. Crépon said. But they are always careful to avoid its extreme xenophobia and its anti-Muslim rhetoric.

“What distinguishes the National Front is its outrageousness, its radicalism,” Mr. Crépon said. The party’s dilemma, never resolved, is that “if it is too radical, it marginalizes itself, but if it normalizes itself, it becomes too commonplace.” As Ms. Le Pen’s father, Jean-Marie, the party’s founder, once remarked, none of its base voters would be interested in a National Front that sounds too tame.

The party’s supporters made that much abundantly clear at a boisterous flag-waving rally here last week. “With all this immigration, and then the immigration leading to terrorism; she said it, and nobody was listening,” said Nellie Viaro, a National Front municipal councilor from the Paris suburbs.

“She’s a woman of conviction who is persecuted by the Socialists,” said Yves Breugnot, a party activist. He added, referring to France’s flag, “With the Socialists, there is no blue-white-red, there is only red.”

There were no big winners in Sunday’s vote, though the ruling Socialists did better than expected, holding on to five regions to the right’s seven and getting just under 30 percent of the vote. Mr. Sarkozy’s party, with just over 40 percent, was hoping to sweep the boards but fell far short, a result interpreted by most pundits as a sign of strength for the Socialist president, François Hollande, in the pre-electoral period before 2017.

France’s stagnant economy and high unemployment have kept Mr. Hollande at rock bottom in the polls for much of his tenure. But he rose in popularity after the Nov. 13 terrorist attacks in Paris, when he was credited with unifying and reassuring a frightened country. That rise was reflected in Sunday’s less than disastrous regional poll results.

Aurelien Breeden contributed reporting.

A version of this article appears in print on , on Page A11 of the New York edition with the headline: Le Pen Remains Defiant Despite National Front’s Trouncing at the Polls. Order Reprints | Today’s Paper | Subscribe